1. The Field of the Invention
The present invention relates to systems, apparatus and methods for a fiber optic package for a fiber coupler. More particularly, the present invention relates to a packaging apparatus for a fiber coupler having a configuration adapted to provide the water and anti-vibration protection required by wavelength division multiplexing couplers.
2. Background and Relevant Art
Fiber optics are increasingly used for transmitting voice and data signals. As a transmission medium, light provides a number of advantages over traditional electrical communication techniques. For example, light signals allow for extremely high transmission rates and very high bandwidth capabilities. Also, light signals are resistant to electromagnetic interference that would otherwise interfere with electrical signals. Light also provides a more secure signal because it does not emanate the type of high frequency components often experienced with conductor-based electrical signals. Light also can be conducted over greater distances without the signal loss typically associated with electrical signals on copper conductor.
Many conventional electrical networks are being upgraded to optical networks to take advantage of the increased speed and efficiency. One of the many required components of an optical network is a fiber coupler. In a fiber coupler, optic fibers are coupled allowing for a variety of functionality required by optical networks. Fiber couplers perform the function of division and distribution of power in a fiber circuit. This division may be independent of wavelength and polarization, as in the case of a star coupler in distributive networks. On the other hand, it may be designed to couple a specific band of wavelengths from one fiber to another, as in a pump multiplexer in an EDFA circuit. One widely used method of forming fused couplers is accomplished by twisting two monomode fibers together, heating in a short region until the fibers fuse, and pulling to taper them down into a coupled structure.
Fiber coupler packaging technologies have developed to provide the additional strength and protection needed to maintain the integrity of the fused fiber couplings. FIG. 1 illustrates a prior art coupler package 1. Coupler package 1 comprises a cylinder 10, first and second seals 20a,b, and anti-vibration rings 30a,b. The coupler package 1 is adapted to provide protection to fused portion 6 of first fiber 2 and second fiber 4.
The cylinder 10 comprises a outer cylinder 12 and an inner sleeve 14. The outer cylinder is made of stainless steel to provide the impact protection, while the inner sleeve is comprised of a non-metallic material to provide temperature and corrosion buffering. Anti-vibration rings 30a,b are comprised of rubber to provide the vibration protection to coupler package 1.
First and second seals 20a,b are adapted to prevent moisture penetration to the interior of the cylinder 10. The first seal 20a is comprised of a first washer 22a, an epoxy element 24a, a second washer 26a, and an epoxy end member 28a. The first and second washers 22a, 26a are comprised of rubber and provide protection against vibration and moisture penetration by forming a seal with the outer cylinder 12. Epoxy element 24a and epoxy end member 28a, form an adhesive coupling with washers 22a, 26a and outer cylinder 12 providing additional moisture penetration protection to the interior of cylinder 10.
The second seal 20b is comprised of a first washer 22b, an epoxy element 24b, a second washer 26b, and an epoxy end member 28b. The first and second washers 22b, 26b are comprised of rubber and provide protection against vibration and moisture penetration by forming a seal with the outer cylinder 12. Epoxy element 24b and epoxy end member 28b, form an adhesive coupling with washers 22b, 26b and outer cylinder 12 providing additional moisture penetration protection to the interior of cylinder 10.
While the coupler package illustrated in FIG. 1 provides some protection against moisture penetration and vibration, the amount of protection is insufficient for some types of couplers and/or in certain conditions. For example, wavelength division multiplexing (WDM) couplers require a higher degree of temperature and water penetration protection than other fiber couplers due to the coupler""s susceptibility to wavelength shifts. The Telecordia reliability test, particularly the 85 degree Celsius and the 85% humidity test, illustrate the shortcomings of traditional fiber coupler packaging configurations in providing the degree of protection needed for substantial durations under severe conditions.
One approach to increase the temperature and humidity strength of fiber couplers has been to utilize a metal sealing configuration. Metal sealing is accomplished by removing the fiber coating of an optic fiber. Evaporated or plated gold is coupled to the fiber. The fiber is then gold soldered to a gold plated module or tube. Additional anti-vibration measures are also provided to the tube or module. The metal sealing provides the necessary water penetration protection while the anti-vibration measures provide the needed vibration protection. While the metal sealing configuration provides some of the needed protection, the manufacturing and other requirements of such couplers increase the size and cost of the coupler and coupler packaging. Additionally, the soldering of the fibers and the removal of the fiber coating can increase the damage and stress to the fiber, reducing the overall strength of the fiber.
In view of the above, it is apparent that there is a need for a new and improved coupler package apparatus. It is desirable that the apparatus provide additional moisture and anti-vibration protection for fused fiber coupling.
These and other problems are overcome by the present invention which is directed to a coupler package providing additional moisture and anti-vibration protection. The coupler package utilizes an inner assembly and an outer assembly. The inner and outer assembly preferably comprise first and second cylinders. The cylinders form an inner chamber and an outer chamber. The inner chamber encloses fused optical fibers while the outer chamber encloses the inner cylinder. The ends of the cylinders are sealed thus providing moisture protection to the sealed fibers. The dual assembly configuration provides additional moisture and anti-vibration protection to the fused fibers of the fiber coupler. The double tube structure increases the penetration length for water and the seals decrease the cross section for water penetration.
In one embodiment, the cylinders are formed from INVAR (a metal alloy that exhibits a nearly zero coefficient of thermal expansion), providing additional temperature and impact protection to the fibers. While maintaining the needed protection, the double tube configuration allows the package to remain small and inexpensive to manufacture. In yet another embodiment, the present invention does not require a metal solder, thus maintaining the integrity of the fused fibers. In another embodiment of the present invention, anti-vibration rings are provided in both the inner and outer assemblies thus providing additional anti-vibration protection.